Wabi warnings during GCC build

Wabi warnings during GCC build

[Steve Ellcey]

Are other people building GCC seeing these messages during the build:

cc1plus: warning: -Wabi won't warn about anything [-Wabi]
cc1plus: note: -Wabi warns about differences from the most up-to-date ABI, which is also used by default
cc1plus: note: use e.g. -Wabi=11 to warn about changes from GCC 7

It doesn't seem to be causing any problems in the build (even bootstrap)
but I am wondering why it is there.  It seems to be happening when
using the latest (just built) g++ to build libstdc++ so it shouldn't
be related to the system GCC that I am using to build with.

I didn't find any mention of it in the gcc or libstdc++ mailing lists
when I looked or find any bugzilla report.

Steve Ellcey

Re: Wabi warnings during GCC build

[Marek Polacek]

On Wed, Jun 27, 2018 at 08:53:48AM -0700, Steve Ellcey wrote:
> Are other people building GCC seeing these messages during the build:
> 
> cc1plus: warning: -Wabi won't warn about anything [-Wabi]
> cc1plus: note: -Wabi warns about differences from the most up-to-date ABI, which is also used by default
> cc1plus: note: use e.g. -Wabi=11 to warn about changes from GCC 7
> 
> It doesn't seem to be causing any problems in the build (even bootstrap)
> but I am wondering why it is there.  It seems to be happening when
> using the latest (just built) g++ to build libstdc++ so it shouldn't
> be related to the system GCC that I am using to build with.
> 
> I didn't find any mention of it in the gcc or libstdc++ mailing lists
> when I looked or find any bugzilla report.

I see it too, started with r261571.
libstdc++/acinclude.m4 needs to be adjusted:
WARN_FLAGS='-Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi'
I guess to -Wabi=11?

Marek

Re: Wabi warnings during GCC build

[Eric Gallager]

On 6/27/18, Marek Polacek <polacek@redhat.com> wrote:
> On Wed, Jun 27, 2018 at 08:53:48AM -0700, Steve Ellcey wrote:
>> Are other people building GCC seeing these messages during the build:
>>
>> cc1plus: warning: -Wabi won't warn about anything [-Wabi]
>> cc1plus: note: -Wabi warns about differences from the most up-to-date ABI,
>> which is also used by default
>> cc1plus: note: use e.g. -Wabi=11 to warn about changes from GCC 7
>>
>> It doesn't seem to be causing any problems in the build (even bootstrap)
>> but I am wondering why it is there.  It seems to be happening when
>> using the latest (just built) g++ to build libstdc++ so it shouldn't
>> be related to the system GCC that I am using to build with.
>>
>> I didn't find any mention of it in the gcc or libstdc++ mailing lists
>> when I looked or find any bugzilla report.
>
> I see it too, started with r261571.

Yeah I also see it.

> libstdc++/acinclude.m4 needs to be adjusted:
> WARN_FLAGS='-Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi'
> I guess to -Wabi=11?
>
> Marek
>

At first I was going to wonder if it wasn't necessary to remain
compatible with old versions of GCC that don't support -Wabi=11, but
then I reread the part about this happening with the just-built GCC,
so if that warning is only ever used with the just-built GCC, then
yeah, I'd guess it'd probably be okay.

Re: Wabi warnings during GCC build

[Jonathan Wakely]

On Wed, 27 Jun 2018 at 17:28, Eric Gallager wrote:
> At first I was going to wonder if it wasn't necessary to remain
> compatible with old versions of GCC that don't support -Wabi=11, but
> then I reread the part about this happening with the just-built GCC,
> so if that warning is only ever used with the just-built GCC, then
> yeah, I'd guess it'd probably be okay.

Libstdc++ is only ever built with the new GCC.

Building it out-of-tree isn't supported.